Adjust examples declaring non-nullable positional optional parameters with no default

Author: eernstg

specification/dartLangSpec.tex

@@ -3413,7 +3413,7 @@ \subsubsection{The Method \code{noSuchMethod}}
 in order to correctly override \code{noSuchMethod} in \code{Object}.
 For instance, it can have signature
 \code{noSuchMethod(Invocation i)} or
-\code{noSuchMethod(Object i, [String s = ''])},
+\code{noSuchMethod(Object i, [String? s])},
 but not
 \code{noSuchMethod(Invocation i, String s)}.
 This implies that the situation where \code{noSuchMethod} is invoked
@@ -4184,7 +4184,7 @@ \subsubsection{Generative Constructors}
 
 \begin{dartCode}
 class A \{
-  int x;
+  int? x;
   A([this.x]);
 \}
 \end{dartCode}
@@ -4195,8 +4195,8 @@ \subsubsection{Generative Constructors}
 
 \begin{dartCode}
 class A \{
-  int x;
-  A([int x]): this.x = x;
+  int? x;
+  A([int? x]): this.x = x;
 \}
 \end{dartCode}
 
@@ -15651,7 +15651,7 @@ \subsubsection{Generic Method Instantiation}
 \}
 \\
 \CLASS{} B \EXTENDS{} /*\,or\,\,\IMPLEMENTS\,*/ A \{
-  X fi<X \EXTENDS{} num>(X x, [List<X> xs]) => x;
+  X fi<X \EXTENDS{} num>(X x, [List<X>? xs]) => x;
 \}
 \\
 \VOID{} main() \{
@@ -15663,7 +15663,7 @@ \subsubsection{Generic Method Instantiation}
 \commentary{%
 \noindent
 The function object that \code{f} is bound to at the end of \code{main}
-has dynamic type \code{int\,\,\FUNCTION(int,\,[List<int>])},
+has dynamic type \code{int\,\,\FUNCTION(int,\,[List<int>?])},
 and it is obtained by implicitly
 ``passing the actual type argument \code{int}''
 to the denoted generic instance method,